Vascular grafts are well known to repair or replace the damaged or diseased portions of body vessels such as blood vessels. It has been a common practice to install crimps in a graft by fully crimping the graft. Crimping provides several advantages. For example, textile grafts are much easier for the surgeon to handle once crimped, because crimping provides a self-supporting feature and keeps the lumen of the graft open during implementation. Additional crimping can provide for increased flexibility and longitudinal extension and contraction, where needed. See U.S. Pat. No. 4,047,252 to Liebeg et al. In certain applications, however, flexibility is desired but significant longitudinal extension is not. Additionally, due to the use of stents in combination with grafts as composite devices, the need for full-length crimping to keep the lumen open during implantation is lessened.
In certain applications, such as endoluminal stent-graft devices used in thoracic, abdominal or peripheral applications, it is disadvantageous to have excessive extension subsequent to implantation. Additionally, use of a “fully crimped” graft on a thoracic stent-graft has identified issues with graft elongation within the deployment sheath causing the graft to not fully recover to its original unloaded length. This is particularly apparent when fully crimped grafts are used in devices which allow the flow of arterial blood pressure to be the force which opens the graft lumen. See U.S. Pat. No. 5,697,970 to Schmitt et al. and U.S. Pat. No. 5,476,506 to Lunn. Fully crimped grafts have a significant degree of unwanted elongation extension therefore creating difficulty during deployment. The graft is delivered in the compressed state in an elongated fashion with a stent. The stent can easily return to its original length due to shape memory properties, but the graft cannot. When full graft length recovery is required, herein lies the problem. The graft expands with the stent at each end of the graft, but due to crimping along its entire length, the graft does not recover to its original length during deployment. Thus, prior devices have not provided a solution which balances the need to accommodate vessel angulation flexibility and to facilitate deployment with the need to minimize longitudinal extension.
It is, therefore, desireable to provide a crimped graft which allows flexibility only where needed, i.e., only use crimping where needed, thereby minimizing undesirable longitudinal extension and requiring less recovery during deployment.